AI-1 Shootout

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Comments

  • hearingimpared
    hearingimpared Posts: 21,136
    edited February 2007
    We bi-amped BDT's SDA at the fest, used a pair of Anthem 150 watt channel amplifiers, more than enough juice. They sounded very nice. The tweets actually draw very little power. I would look for an amp with a fast slew rate to capture quick transients.

    You just have to try bi-amp to see how you like it, I mono-bridged the 1C's with the Stancor transformer, I used a pair of NAD 2700, bridged they ran at 440 or something like that with headroom so high I just cant remember. The 1C cannot be biamped.

    Anyway, I found the 1C's sounded better this way with the Stancor Transformer than with the straight cable and a single NAD 2700. As suggested I suspect this is do to the increased available power overcoming any signal loss with the transformer. I wary that the sound might be gritty in the bridged mode, however, this was simply not the case, I would say the NAD are on the warm side of things, not the most detailed of amps, but quite musical, one of favorites for sure.

    RT1

    This brings me back to my stereo electronics 101 classes in tech school a long, long time ago. There is another benefit to horizontal bi-amping. When you play discs like Telarc's 1812 overture, the cannon blasts have less chance of frying your tweets 'cause you have the low frequencies on a separate amp hence the distorion that may be caused by clipping or overdriving, stay localized at the woofer end.

    Thanks for this post Ted, I forgot about how important the slew rate is or can be.
  • riglehart
    riglehart Posts: 276
    edited February 2007
    have less chance of frying your tweets 'cause you have the low frequencies on a separate amp hence the distorion that may be caused by clipping or overdriving, stay localized at the woofer end.

    That is a very good point! The tweets stay on clean power, no matter what's going on below.
    Jolida Tube
    Polk 11T, 7, 5, 5jr, 4
    Standard equip not worth bragging about.
  • PolkWannabie
    PolkWannabie Posts: 2,763
    edited February 2007
    riglehart wrote:
    That is a very good point! The tweets stay on clean power, no matter what's going on below.
    Really ? ... Even without an active crossover between the pre/pro and amp ?

    Without an active crossover prior to the amp I would think that each set of speaker terminals would be getting the full range signal to the speakers crossovers to deal with.
  • riglehart
    riglehart Posts: 276
    edited February 2007
    Without an active crossover prior to the amp I would think that each set of speaker terminals would be getting the full range signal to the speakers crossovers to deal with.


    You are correct, both top and bottom do get PRESENTED with the full spectrum of signal. However, due to the crossover in the speaker, they only ACCEPT what they are designed for. The way I think of it is that the speakers & crossover actually provide "back pressure" to your amp, and the amp can only send what is easily received by that section of the speaker. When you disconnect the jumpers on the speaker for top/bottom biamping, I am pretty sure you have just effectively disconnected the top/bottom drivers.

    Think of what happens when you have no speakers on the amp (infinite resistance at all frequencies). You can crank the volume all the way up and your amp does no work at all. It would if it could, but it can't. Now short them out (dumb idea), now with zero resistance the amp goes into protected mode immediately (or worse) because it has nothing stopping it.

    Finally, hook a speaker up and it will start passing signal through AS THE SPEAKER WILL ACCEPT IT. When you biamp top/bottom, the top crossovers don't allow the lows in and the bottom don't allow the highs in. The crossover creates a "back pressure" on your amp at select frequencies.

    Does that make sense?
    Jolida Tube
    Polk 11T, 7, 5, 5jr, 4
    Standard equip not worth bragging about.
  • PolkWannabie
    PolkWannabie Posts: 2,763
    edited February 2007
    There is no back pressure per se ... There's nothing in the speakers ( Crossovers ) sending a signal back up the speaker wire to your amp telling it not to bother sending signals above/below some particular threshold.

    Unless the amp does not receive some particular range of frequencies because they have been cut off by an active x/o, then they'll still be there ... If that signal because of some reason has distortion in it, then it'll still be there ...
  • madmax
    madmax Posts: 12,434
    edited February 2007
    I've always thougt seperate amplification for the bass and treble was a good idea because if you run out of juice because of the bass (or the treble) it doesn't affect the power available to the other. I hadn't really considered that if a bass signal distorts, that distortion may be in the treble region and get routed to the tweeters if using a single amp. Very good point and yet another thing to consider.
    madmax
    Vinyl, the final frontier...

    Avantgarde horns, 300b tubes, thats the kinda crap I want... :D
  • reeltrouble1
    reeltrouble1 Posts: 9,312
    edited February 2007
    Or........use an amplifier that has adequate power to drive a signal without distorting.

    RT1
  • madmax
    madmax Posts: 12,434
    edited February 2007
    Everything distorts when a pin drops.
    madmax
    Vinyl, the final frontier...

    Avantgarde horns, 300b tubes, thats the kinda crap I want... :D
  • hearingimpared
    hearingimpared Posts: 21,136
    edited February 2007
    There is no back pressure per se ... There's nothing in the speakers ( Crossovers ) sending a signal back up the speaker wire to your amp telling it not to bother sending signals above/below some particular threshold.

    Unless the amp does not receive some particular range of frequencies because they have been cut off by an active x/o, then they'll still be there ... If that signal because of some reason has distortion in it, then it'll still be there ...


    The problem is not that the preamp cliping or distorting, it is the AMPLIFIERS that the distortion takes place.

    If I took my mono blocks from a Y connector on the left and right out of my preamp and used one to power the left speakers lower posts and the other to the right channels lower posts, then from those same Y connections on the preamp go to let's say a stereo tube amp (this assumes the jumpers have been removed) and place the left channel on the speakers upper posts and the right channel on that speakers up posts, a blast from that 1812 overture cannon would be nailing the bass frequencies the hardest so if the mono blocks on the lower posts clip or distort terribly it would not have any effect on the tube amplifier powering the two speakers upper posts where the high frequencies are played.

    I think that makes this whole debate a little simpler, no?
  • PolkWannabie
    PolkWannabie Posts: 2,763
    edited February 2007
    Yes, I'm well aware that potential clipping takes place in amplifiers ...

    Simpler ? ... Maybe ... But I can't say that I see this as any real difference ...

    From your example, without an active x/o the tube amp and the mono blocks are getting the same full frequency signal to amplify and individually they either clip or they don't.

    If the tube amp you are using to drive the highs doesn't clip attempting to amplify the full frequency signal then no problem ... If it does then potentially you do have a problem ...
  • reeltrouble1
    reeltrouble1 Posts: 9,312
    edited February 2007
    No Joe......waaaaaaaaaa!!!!!!!!!!!

    It is quite possible to overdrive the tweeters with clean power in a bi-amp config. Don't take it wrong, I like bi-amping in general, just something to keep in mind if you do it and crank the gain thinking your tweets are completely safe.

    RT1

    RT1
  • hearingimpared
    hearingimpared Posts: 21,136
    edited February 2007
    Yes yes gentlemen you are correct. Over driving tweets is not where I want to be. However my understanding of the lows is that they require much more wattage than the tweets do, so I am deducing that if I use 300 wpc on my low frequencies and 100 to 200 wpc on my highs, I'm less likely to blow my tweets because my low frequency amps have sufficient power to handle the wide dynamic range of say the Telarc 1812 Overature CD or LP (LP of course is more prone to distortion just because of the nature of stylus to record), yes????

    PolkWannabie didn't we have the active xover conversatation back in the summer? I seem to remember you building an active xover for your rig.
  • riglehart
    riglehart Posts: 276
    edited February 2007
    There is no back pressure per se ... There's nothing in the speakers ( Crossovers ) sending a signal back up the speaker wire to your amp telling it not to bother sending signals above/below some particular threshold.

    Unless the amp does not receive some particular range of frequencies because they have been cut off by an active x/o, then they'll still be there ... If that signal because of some reason has distortion in it, then it'll still be there ...

    Yes there is. You are right, the speaker crossover does not send a signal "back up the speaker wire", but it does impede the signal and provide a load to the amp. This impedence can (and almost always will) vary depending on the frequency. A speaker crossover is made primarily from inductors, which inhibit high frequencies, and capacitors, which inhibit low frequencies. The size and combination of these (which Matthew Polk is very clever about) dictate which signal is ALLOWED to go to each driver. A good crossover takes the entire 20-20k frequency and spreads the load out across the drivers so they share the load and only work on the portion of the 20-20k that they are designed for. You can also take this one step further and the crossover can impede certain frequencies totally. This is exactly what top bottom biamping does.

    If you hook your 500 watt amplifier up to your tweeter's crossover network, your amp will not be required to DRIVE any frequencies below what the crossover is designed for. Even though your amp has the full 20-20k being fed to it by the source, the impedence of the speaker crossover is very high at low frequencies (from the capacitors) and the amp does not have to do any work to create this low frequency current. That's why in general you need a more powerful amp for low impedence speakers and subwoofers. Low impedence speakers require an amp that can really pour out the current. However high impedence speakers on that same amp will draw less current, and be an easier load. The same thing goes for the entire spectrum of audible sound. An amp only does the work that it needs to, depending on what the speaker crossover accepts.

    It is counter intuitive, but the more impedence your speaker has, the less current your amp has to create AT ANY GIVEN FREQUENCY. Another way to say it is, the more impedence your speaker has, the less current your amp CAN create AT ANY GIVEN FREQUENCY. (has to / can) are interchangable.
    Jolida Tube
    Polk 11T, 7, 5, 5jr, 4
    Standard equip not worth bragging about.
  • PolkWannabie
    PolkWannabie Posts: 2,763
    edited February 2007
    Joe,

    I don't recall having this discussion with you last summer as I wasn't actively posting then and no I don't have an Active X/O for my rig. The SRT satellites offer different ways to biamp, triamp and/or biwire then most speakers with the chief additional difference being that the SDA & Stereo arrays can be separately amplified. When this approach is used the satellites are an 8 ohm load as opposed to their normal 4 ohm load. The tweets can also be biwred or separately amplified.

    Riglehart,

    Good explanation and probably more accurate/appropriate then mine ... Thanks ...

    This is a difficult ( at least for me ) topic to get a handle on how the various pieces work together which is not simplified by the articles available as there doesn't seem to be agreemnt between the opinions even though one would think this aspect would be relatively straight forward i.e. it either works this way ... or that way ...
  • madmax
    madmax Posts: 12,434
    edited February 2007
    Amplifiers can clip pretty easy even when they are only driving tweeters. Its because you may overshoot the voltage rails, not because you are trying to draw too much current. You could have more power than you are using (since you are only using a small portion of the bandwidth) and still call for a higher voltage than you have available. When that happens it clips.
    madmax
    Vinyl, the final frontier...

    Avantgarde horns, 300b tubes, thats the kinda crap I want... :D
  • riglehart
    riglehart Posts: 276
    edited February 2007
    madmax wrote:
    Its because you may overshoot the voltage rails, not because you are trying to draw too much current.

    Hmm. I want to understand this. So, if you look at a voltage sine wave at a high frequency, you are saying that if you try and amplify that sine wave past the voltage limit the transistor can reproduce/control. It clips. I'm trying to remember back to my electronics in college.

    Clipping is DC current, right? Because the transistor looses control of itself.
    Jolida Tube
    Polk 11T, 7, 5, 5jr, 4
    Standard equip not worth bragging about.